Software is being written to control the operation of processors, including microprocessors, in a wide variety of fields. As software becomes more complex and lengthy, the probability of software errors or "bugs" increases. Furthermore, the difficulty of finding software bugs increases with this increased length and complexity of software. While bugs that prevent execution of the software will be apparent, other types of bugs merely effect the performance or efficiency of the software without preventing its execution. Software bugs that merely effect the execution of the software may easily go undetected, thus indefinitely impairing the efficiency of the software. For example, software may allocate memory resources in an inefficient manner thus preventing the software from running at optimum speed. However, since the software continues to execute, the existence of these memory allocation errors will not be apparent.
A number of techniques have been developed to analyze the performance of software in an attempt to find software bugs, including software bugs that merely effect the performance of the software execution. One traditional technique is instrumented source code in which executable tag statements are inserted into various branches and locations of source code, thereby "instrumenting" the source code. After the source code has been compiled and linked, the tag statements are executed along with the code. As each tag statement is executed, it performs an operation that can be either detected by an analysis device or recorded for later examination. For example, each tag statement may write a value to a respective address so that the identity of the address containing that value provides an indication of which tag statements were executed. As another example, each tag statement may print tag identifying data to a disk file. As still another example, an array can be reserved in memory, with each array element corresponding to a tag inserted in a respective location in the source code. As each tag is executed, it sets a corresponding bit in the array. One approach to analyzing software with instrumented code is described in U.S. Pat. No. 5,265,254 to Blasciak et al.
Using instrumented code, a wide variety of software parameters can be analyzed. Not only can instrumented source code allow one to determine which branches have been executed, but it can also determine the execution time of a branch or function by placing executable tag statements at the entry and exit points of the branch or function. When these tag statements are executed, they generate respective tags which are time stamped so that the elapsed time between executing the tag statements can be determined.
Although instrumented code is often a useful technique for analyzing the performance of software in a general purpose (i.e., "host") computer system, it is less suitable for analyzing the execution of software in an embedded system. An embedded system is a system whose primary purpose is to perform a specific function rather than to perform general computational functions. For example, a microprocessor-based microwave oven controller, a microprocessor-based automobile ignition system, and a microprocessor-based telephone switching system are all embedded systems. Embedded systems do not lend themselves to instrumented code for several reasons. First, embedded systems generally do not have mass storage devices, such as disc storage, to store the result of tag statement executions. While the result of executing a tag statement can be stored in on-board random access memory, it is often difficult to externally retrieve such information. Furthermore, storing the results of tag statement executions in system memory consumes system memory resources thus preventing the target from executing the software in a normal manner. It is generally desirable to test the performance of software in an embedded system under the same conditions that the software will normally run. Thus, an ideal software analysis technique would be "transparent" to the target system and thus have no effect on the manner in which the target system executes software. For these reasons, instrumented code is generally not suitable for analyzing software in an embedded system.
In addition to software-based software analysis techniques (e.g., instrumented code), hardware-based techniques have been developed to analyze software executing in embedded systems. For example, logic probes have been placed on the address and data bus lines of microprocessors in an attempt to observe the execution of software in embedded systems. However, it is very difficult to monitor the execution of software using logic analyzers, and the lack of any data reduction on the output of the logic analyzer makes this technique very time-consuming. Furthermore, it is not always possible to determine which instructions are being executed using the logic analyzer. For example, processors executing instructions from internal cache memory cannot be monitored using a logic probe because the execution of these instructions is not reflected on externally accessible busses.
Another hardware-based technique for analyzing the performance of software in embedded systems uses an emulator in connection with instrumented code. Basically, this technique uses an emulator to monitor the execution of tag statements thus eliminating the need to consume system memory resources and providing a means to extract tag execution data. One example of this approach is described in U.S. Pat. No. 4,914,659 to Erickson. As described in the Erickson patent, tag statements are inserted in the source code and executed in an emulator connected to the target system. Each of the tag statements writes a variable to a respective unique address. The emulator monitors the address bus of the emulated processor to detect addresses on the address bus corresponding to the respective tag statements. While the approach described in the Erickson patent does extract the tag execution data without consuming system resources, it nevertheless suffers from a number of limitations. For example, by requiring that there be a unique address reserved for each tag statement, overlay memory techniques must be employed and a substantial amount of the target system's address space is consumed.
Another hardware approach to analyzing software executing in an embedded system is described in U.S. Pat. No. 4,937,740 to Agarwal et al. The Agarwal et al. patent discloses a software analysis system in which a hardware probe monitors the address bus of the target system to capture addresses. The system disclosed in the Agarwal et al. patent includes an internal tag generator that generates tags when respective addresses (up to 256) selected by the user are captured by the probe. Since the Agarwal et al. system does not use instrumented code techniques or otherwise correlate tags generated from the captured addresses with respective software locations, the Agarwal et al. system does not provide easy to use and understand information about the execution of the software.
There is therefore a need for a method and apparatus that can analyze the execution of software in an embedded system without the requirement that the embedded system have on-board data storage and/or output port capabilities in a manner that does not consume system resources, including memory, processor time and I/O resources, of the target system.